A description of a magnetic step-analyser of intense relativistic electron beam energy spectra is presented. The azimuthal magnetic field in the analyser is created by the current flowing through two coaxial cylinders. The particles move in the analyser along the trajectories, representing spirals with the pitch depending on the energy and rolled on the magnetic field spiral force lines. The magnetic analyser serviceability is demonstrated at the U-1 device with 1.1 MeV electron beam energy and 50 kA current. 6 refs.; 7 figs.; 2 tabs.